Communications protocol for mobile device

ABSTRACT

A communication device and method for operating the same includes a GPS receiver that periodically generates a position signal, a wireless modem transmitting or receiving messages and a controller that is coupled to the receiver and the modem. The controller discontinues operating the wireless modem when the GPS signal generates the position signal and vice versa to reduce interference with the other device.

RELATED APPLICATIONS

[0001] The present invention is related to applications (Attorney DocketPD-02-0667) entitled “Communication System For Tracking Assets”;(Attorney Docket PD-02-1094) entitled “Method And Circuit ForInitializing Non-Volatile Memory”; (Attorney Docket PD-02-1095) entitled“Programmable Messages For Communication System Having One-Button UserInterface”; (Attorney Docket PD-02-1097) entitled “One-Button UserInterface For A Portable Device”; and (Attorney Docket PD-02-1221)entitled “Serial Port Multiplexing Protocol”; filed simultaneouslyherewith and incorporated by reference herein.

TECHNICAL FIELD

[0002] The present invention relates generally to a communicationsystem, and more particularly, to a communication protocol to maximizereliability in communications between a base station and a mobile unit.

BACKGROUND ART

[0003] Companies and governmental entities that employ mobile unitsoften have difficulty locating the units. The units in turn often havedifficulty knowing their position. In operations such as fighting forestfires or other types of wildfires, knowing the position of ground unitsis desirable to better manage the changing requirements for fighting thefire. A simple, reliable system for tracking assets and communicatingback and forth therewith is thus desirable.

[0004] Reliability is an important factor when providing communicationsystems, particularly in life-threatening situations such as forestfires. Communications must be reliable. Typically, if communications ina mobile system are sent but not received, no indication is present toeither party that the message has not been received.

[0005] It would therefore be desirable to provide a system that providesreliable communications and acknowledgements that messages have beenreceived.

SUMMARY OF THE INVENTION

[0006] The present invention provides a communications protocol forcontrolling communications between a mobile unit and a base station.

[0007] In one aspect of the invention, a method of operating acommunications device includes providing power to the device, while awireless modem is off turning on a GPS receiver. The method furthercomprises waiting a predetermined amount of time and receiving a GPSsignal. After the GPS signal is received, turning off the GPS receiverand turning on the wireless modem.

[0008] In a further aspect of the invention, a communication deviceincludes a GPS receiver that periodically generates a position signal, awireless modem transmitting or receiving messages and a controller thatis coupled to the receiver and the modem. The controller discontinuesoperating the wireless modem when the GPS signal generates the positionsignal. Thereafter, the controller operates the wireless modem.

[0009] One advantage of the invention is that potential interferencebetween the GPS receiver and the wireless modem is eliminated. Thisallows more reliable communication between a base station and the deviceas well as more reliable reception of GPS signals and hence betteraccuracy of position determination.

[0010] Other aspects and advantages of the present invention will becomeapparent upon the following detailed description and appended claims,and upon reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is a block diagrammatic view of a communication systemformed according to the present invention.

[0012]FIG. 2 is a perspective view of a mobile unit according to thepresent invention.

[0013]FIG. 3 is a top perspective view of the mobile unit of FIG. 2.

[0014]FIG. 4 is a block diagrammatic schematic view of a mobile unit.

[0015]FIGS. 5A, 5B, and 5C are alternative embodiments for theantenna/cap assembly for a mobile unit.

[0016]FIG. 6 is a block diagrammatic schematic view of a base stationaccording to the present invention.

[0017]FIG. 7 is a screen printout of a display of the base station ofFIG. 6.

[0018]FIG. 8 is a block diagrammatic schematic view of the interface ofthe base station of FIG. 6.

[0019]FIG. 9 is a flow chart of the operation of the base station.

[0020]FIG. 10 is a schematic representation of three banks of memoryused in the present invention.

[0021]FIG. 11 is a flow chart of a memory initialization of the presentinvention.

[0022]FIG. 12 is a representation of a text display for a mobile unit.

[0023]FIG. 13 is a flow chart of a method to update outgoing messages ofa mobile unit.

[0024]FIG. 14 is a flow chart of the operation of the mobile unit.

[0025]FIG. 15 is a flow chart of the operation of the mobile unit whenreceiving a message.

[0026]FIG. 16 is a flow chart of the operation for receiving a messagein a mobile device.

BEST MODES FOR CARRYING OUT THE INVENTION

[0027] In the following figures the same reference numerals will be usedto identify the same components.

[0028] The following description is illustrated and described withrespect to a two-way communication system. However, the presentinvention has various features that may be used in other types ofelectronic devices including other electronic communication devices.

[0029] Referring now to FIG. 1, the communication system 10 isillustrated having a base station 12 that communicates with variablemobile units 14. The mobile units 14 illustrated are a handheld user 16and a vehicle user 18. While only two units 14 are illustrated, severalmobile units 14 may be provided in the communication system 10. Forexample, in one constructed embodiment, up to 999 mobile units were ableto be provided. Of course, that number may be easily increased. Basestation 12 and mobile units 14 communicate with each other using two-waycommunication signals 20. The two-way communication signals may containmessage signals, paging signals, position signal, status inquirysignals, and the like. Communication signals 20 are used to provideinformation from the mobile users 14 to the base station 12 and from thebase station to the mobile users. The base station 12 ultimately tracksand displays the position of each of the mobile units 14.

[0030] GPS satellites 22 transmit signals that are received by mobileunits 14 and base station 12 so that each may determine their positionrelative to the latitudinal and longitudinal positions of the earth. Theglobal positioning system, the multitude of satellites, and thetriangulation techniques to ascertain longitude, latitude, and elevationof a user are well known.

[0031] Referring now to FIG. 2, the mobile unit 14 is illustrated. Inthis configuration, mobile unit 14 is handheld user 16. Handheld user 16has a sealed housing 26 that has a battery portion 28, a control anddisplay portion 30, and an antenna mount/cap assembly 32. The batteryportion 28 and the control and display portion 30 are coupled togetherusing a connector 34 positioned therebetween. Connector 34 may beexposed if battery pack 28 is removed and a direct power source iscoupled thereto. Such an application may be used in a vehicle mountedunit so that the power supply for the rest of the unit becomes thevehicle's power supply.

[0032] The control and display portion 30 includes a display 36. Display36 is preferably a text display. In one constructive embodiment, display36 was a backlit LCD display. As a default, display 36 displays positioninformation thereon. As will be further described below, when messagesare received from the base unit the message signals may be displayed ondisplay 36 as well.

[0033] Antenna mount/cap assembly 32 is an interchangeable unit. Theantenna mount/cap assembly has an antenna or connector for an antennafor a GPS system and an antenna or connector for an antenna for awireless modem system as will be further described below. Asillustrated, a wireless modem antenna 38 is provided thereon. A singlebutton interface 40 is also disposed on antenna mount/cap assembly. In aconstructed embodiment, the single button interface 40 was positionednear wireless modem antenna to help prevent inadvertent activation ofthe single button interface 40. Single button interface 40 has anextended and compressed position that are used to control the controland display portion 30 which ultimately controls the transmission ofmobile unit message signal through the wireless modem antenna 38.

[0034] To make the handheld device vehicle mounted, a clip or otherfastener may be used to fix the housing to the vehicle. However,removing the battery pack 28 and powering the unit with the vehiclepower supply may be performed. Also, the antenna mount/cap assembly maybe replaced so that vehicle mounted antennas may be employed.

[0035] Referring now to FIG. 3, a perspective top view of the antennamount/cap assembly is illustrated showing the relative position ofsingle button interface 40 and wireless modem antenna 38.

[0036] Referring now to FIG. 4, a block diagrammatic view of a mobileunit 14 is illustrated. Mobile unit 14 includes a microcontroller 44that is preferably microprocessor-based. The microcontroller 44 controlsthe operation of timing between the mobile unit 14 and the base station.The microcontroller 44 may also set the hopping pattern as describedbelow.

[0037] Microcontroller 44 is coupled to a GPS receiver 46 and a wirelessmodem 48. Both the GPS receiver 46 and wireless modem 48 areelectrically coupled to antennas or connectors within antenna mount/capassembly 32 as described below. GPS receiver 48 provides positionsignals to microcontroller 44. Wireless modem 48 transmits and receivesvarious types of message signals, inquiry signals and position signalsthereto and therefrom. Thus, wireless modem 48 acts as a transceiver.Wireless modem 48 may also have a microcontroller 50, which in turn iscoupled to a memory 52. The modem 48 may, for example, be a 902-928 MHzfrequency hopping spread spectrum modem. Each modem may, for example,generate 115.2 Kbaud and may sustain a 80 Kbits/second information flow.Memory 52 may, for example, be non-volatile memory such as EEPROM.Microcontroller 44 is also coupled to single button interface 40, amemory 54 that may, for example, store various information such as aserial number. Microcontroller 44 is also coupled to text display 36which may include an illuminator 56. Memory 44 may be a separatecomponent or may be incorporated into microcontroller 50.

[0038] Microcontroller 44 may also be coupled to a power managementsystem 58 that includes connector 34 that connects the microcontroller44 to a power source 60. As mentioned above, power source 60 may includea rechargeable battery such as a nickel cadmium battery. The batterypack may be formed to be a standard type of battery pack such as the LosAngeles County Fire Department's Bendix/King radio battery pack. Thepower source 60 may include a charge connector 62 used to charge thebattery from a rechargeable power source.

[0039] Microcontroller 44 may also be coupled to a beeper 64 thatgenerates an audible tone for the unit operator. Beeper 64 may includevariable tones. Microcontroller 44 may be programmed to vary the lengthor the timing of the tones to ensure the unit operator receives thesignals. Beeper 64 may signal the presence of a message from the basestation.

[0040] Microcontroller 44 may also be coupled to a timer/clock circuit66. Timer/clock circuit 66 may used to time varied functions such as thelength of time beeper 64 may be operated. Also, clock 66 may be used todetermine when the GPS receiver 46 is to obtain a new position signal.Timer/clock circuit 66 may be a separate component or incorporatedintegrally with microcontroller 44.

[0041] Mobile unit 14 may be positioned within a sealed housing 68.Preferably housing 68 is formed to provide rigidity and reliability tothe system. In one constructed embodiment, a sealed aluminum closure wasused for housing 68. Antenna mount/cap assembly 32 and battery portion28 may also be formed in a similar manner. That is, all the componentsare preferably waterproof and shock resistant.

[0042] Referring now to FIG. 5A, a first embodiment of an antennamount/cap assembly is illustrated. In this embodiment, a GPS receiverantenna 70 and a wireless modem antenna 38 are incorporated therein.

[0043] Referring now to FIG. 5B, a second embodiment of antennamount/cap assembly 32 b is illustrated. In this embodiment, a GPSantenna 70 is provided with a modem connector 72. Modem connector 72 maybe used to interface to an external antenna (not shown).

[0044] Referring now to FIG. 5C, a third embodiment of an antennamount/cap assembly 32 c is illustrated. In this embodiment, a GPSantenna connector 74 is used together with a modem connector 72. Thisembodiment is particularly suited for a vehicle user 18 so that both anexternal GPS antenna and an external modem antenna may be coupledrespectively to GPS antenna connector 74 and modem connector 72.Vehicles may have externally mounted antennas to which the antennamount/cap assembly may be connected.

[0045] Referring now to FIG. 6, base station 12 is illustrated infurther detail. Base station 12 may have at least a portion incorporatedinto a laptop computer 76 or other type of common enclosure. Basestation 12 includes a microcontroller 78 that is also preferablymicroprocessor-based and controls the operation of base station 12.Microcontroller 78 includes a map display 80. Map display 80 may be thescreen of the laptop computer that is used to plot the base stationposition and the positions of the mobile units. Microcontroller 78 mayinclude a data input device such as a keyboard 80, which is standard onlaptop computers. A memory 82 may be incorporated into microcontroller78 or formed as a separate unit. Memory 82 may have a portion that isnon-volatile such as an EEPROM. Microcontroller 78 may also be coupledto a power source 84. Power source 84 may, for example, be a DC sourcebetween 6 and 35 volts. One example of a suitable power source is arechargeable battery.

[0046] Microcontroller 78 may also have a serial port interface 86 sothat microcontroller 78 may couple to other devices such as GPS receiver88 and master wireless modem 90. Both GPS receiver 88 and masterwireless modem 90 may be coupled to an antenna mount 92. Master wirelessmodem 90 may include a microcontroller 94 and a memory 96 to control theoperation thereof. Microcontroller 78 is used to transmit messagesthrough master wireless modem 90. In response to messages received frommaster wireless modem and GPS receiver 88, microcontroller 78 controlsthe map display 80.

[0047] The base station 12 communicates with each mobile unit. Examplesof configuration commands from base station to a mobile unit include:#SHssss0nn Set hopping pattern to nn. #SUssssnnn Set unit's unit addressto nnn (1-999). #SNssssnnn Set unit's network address to nnn (0-254).#SSssssnnn Set the system's sleep time to nnn (0-999). #STssssxxn Setthe system's type ID to n (0-9). #SQssssxxx Set the modem to “Quick On”mode, where the modem links to the network immediately after power-up.#SDssssnnn Set the unit's current system default register to the decimalvalue nnn (0-255). Currently, if bit 0 of this number is 1, this tellsthe unit it has an external comm. antenna, and the GPS is left poweredon all the time. If bit 1 of this number is 1, this tells the unit tostore fixes that do not get acknowledged by the base station. Bit 2turns on and off the repeater configuration. Bit 2 = (1/0) turns therepeater mode for this unit on/off. Bit 3 turns on and off “quiet mode”for the unit. When “quiet mode” is on, the unit does not sound a shortbeep every time it transmits its position. Bit 3-(1/0) turns “quietmode” on/off. #SGssssxxx This puts the unit in GPS test mode, where adirect link is provided between the wireless modem and the GPS.#XCssssxxx Exit configuration mode. #CFssssxxx Clear this unit'sback-logged (stored) fixes that were not acknowledged. #WSssssxxx Writethe contents of the system default register to non-volatile memory sothe current settings will be used even when the power is cycled off thenback on.

[0048] In the above commands, any time a # is entered, the system beginsparsing a new command. So, if the user makes a mistake typing, he/sheshould simply re-type the command starting with #. Also, the commandcharacters can be upper-case or lower-case, either will work. Each“ssss” string is a 4-digit hexadecimal number representing the unit'sserial number. As said above, serial number 0000 is recognized andprocessed by all units, so it is a way of globally configuring all unitswith a single command. The “xxx” strings above are “don't care”sequences, and can be anything—they are ignored by each unit.

[0049] After the configuration mode is exited or if no configurationcommands are received, the system enters the normal operation mode.

[0050] Referring now to FIG. 7, a representative example of a screenoutput of map display 80 is illustrated. As can be seen, screenindicators representing mobile units 14 (handheld users 16 and vehicleusers 18) are illustrated relative to base station 12. Vehicle users 18may have a trail 19 therebehind illustrating past movement. Mobile users16 have a trail 17 therebehind indicating past positions. Thesepositions make the map a “moving map.” Other screen indicators such asmap lines 78 illustrate terrain characteristics, roads, and elevationalchanges in the terrain. As messages are received from mobile units 14, apop-up box 100 may illustrate the various messages such as a distresscall from user terminal having a specific address 102. The address maybe numerical or descriptive as set by the base station operator. Forexample, the mobile unit's operator name may be displayed. Other screenindicators such as colors, flashing symbols and the like may be used tohighlight the relative positions of the various resources to be kepttrack of by base station 12. It should be noted that address 102 maycorrespond to the address of serial number of the mobile unit 14.

[0051] Referring now to FIG. 8, serial port interface 86 is illustratedin further detail. Serial port interface 86 has a microcontroller 104that is coupled to GPS receiver 88 and master wireless modem 90. Themicrocontroller 104 has various inputs RB0 through RB7. The variousinputs are coupled to the wireless modem 90 and the GPS receiver 88.Various outputs of wireless modem 90 are also coupled to a levelinterface 106. Level interface receives signals from microcontroller 104and wireless modem 90. Level interface 106 is coupled to a connector 108such as a serial port connector. More specifically, an RS232 connector108 is illustrated. Such a connector is electrically coupled to themicrocontroller 78 of the base station 12. The pins of the connector 108in one constructed embodiment are coupled as follows: pin 1 is a datacarrier select line from the microcontroller 104; pin 2 is a receiveline relative to the computer; pin 3 is a transmit line from thecomputer; pin 4 is a data terminal ready line from the wireless modem90; pin 5 is a signal ground; pin 6 is a data set ready from thewireless modem; pin 7 is a request to send signal from themicrocontroller 104; pin 8 is a clear to send signal from themicrocontroller; pin 9 is a ring indicator which also comes frommicrocontroller 104. Both the outputs of the GPS receiver 88 and thewireless modem 90 are in serial form. A clock 110, such as an 18.432 MHzclock is also coupled to microcontroller 104. This aspect of theinvention uses the built-in universal asynchronous receiver/transmitter(UART) of microcontroller 104 to monitor all the serial data coming fromthe wireless modem and to relay this information to the base station 12.Essentially, microcontroller 104 allows a pause to be placed on theinformation coming from wireless modem 90 that is destined for RS232connector 108 and allows a GPS message 88 to be inserted therein. Duringsuch hold period, the wireless modem stores information received overthe wireless modem 90 and transmits it through microcontroller 104 toRS232 connector 108 after the GPS signal is received. The presentinvention is hooked up so only information from the GPS receiver 88 maybe inserted within the wireless modem stream by pausing the data fromthe wireless modem 90. However, those skilled in the art will recognizethat a reverse scenario may be set up wherein the transmit line from thebase station may also be routed through the microcontroller so thatinformation may be inserted therein. However, in this constructedembodiment, this feature was not necessary or required.

[0052] Referring now to FIG. 9, the operation of the serial portinterface 86 is illustrated. In step 120, wireless modem signals arereceived from wireless modem 90. The wireless modem signals are coupledto the base station 12 in step 122. When a GPS signal is received instep 124, the wireless modem is told to hold the modem signals. That is,the modem has an internal buffer which is used to store the data whilethe GPS signal is being received. When the modem is told to hold in step126, the RTS line of the modem 90 is de-asserted so that the modem knowsto hold its data. The data from the wireless modem may be thought of asa first plurality of data that is interrupted with a GPS signal. Thatis, the data from the wireless modem has a first data before the GPSsignal and second data after the GPS signal.

[0053] In step 128, the GPS position signal is reconfigured. The GPSsignal is formatted like a wireless modem signal that has an identifierthat indicates that the signal is from the base station. Thus, when thebase station receives the signal, it is plotted on the map display justas any other wireless modem signal. Thus, the base station is trickedinto thinking that the data from the GPS receiver 88 is from wirelessmodem 90. The reconfigured GPS signal is thus coupled to base station instep 130. In step 132, the modem operation is resumed by reasserting theRTS line. Thus, normal two-way data transfer is thus resumed throughwireless modem 90. Also it should be noted that because the base stationrecognizes the ID code as being from the base station, an acknowledgesignal for the position signal of the base station from GPS receiver 88is not performed. It should also be noted that the wireless modemsignals have a wireless modem format. The GPS signal is converted to awireless modem format signal essentially to trick the base station intothinking it is coming from the wireless modem.

[0054] Referring now to FIG. 10, the program memory may be divided upinto various banks: bank 0, bank 1, and bank 2. Bank 2 may, for example,contain the initialization portion 134 while the operational portion 135may be positioned in bank 1. The microcontroller 44 of the mobile unit14 begins executing the program address at 0000. In the presentconfiguration there is room for four instructions between 0000 and 0003,while address 0004 is reserved for interrupts. Thus, the first fourmicrocontrollers instructions are as follows: reset org 0.0000 ;Resetstarts here. bsf pclath,4 ;The B2init subroutine is in Program MemoryBank 2. Icaddr call B2init ;The B2init routine sets up Defaults thenerases this call. bcf pclath,4 ;Back to Program Memory Bank 0. gotostart ;Start running. org 0.0004 ;This is the interrupt vector. Anyinterrupt brings us here. ;The only interrupt expected is a start bit onRB0/INT.

[0055] It should be noted that calling either bank 1 or bank 2 requiresonly setting one bit in the pclath instruction. Thus, only twoinstructions are required. Thus, it is not desirable to put the routinein bank 3 because an extra bit requiring more than one instruction wouldbe required.

[0056] Referring now to FIG. 11, the initialization routine isillustrated. In step 136, the system is powered up. On power up thesystem display may be set to display identifying information such as itsnetwork address, unit address, primary hopping pattern, secondaryhopping pattern, and encryption key. If this is a first power up in step138, step 140 is executed. This decision block will actually take careof itself as will be further described below and is not an actual step.In step 140 the memories are initialized. In step 142, the wirelessmodem memory is initialized. In step 144, the program modifies itselfusing a “no operation” instruction. From the program code describedabove, the B2init routine sets up default and then erases the call bychanging the call to a no operation instruction. That is, the program ismodified so that the icaddr address is set to zero, which is a nooperational instruction. Thus, the next time the system is powered upthis instruction will be skipped since now it is a no operationinstruction. The initialization program thus never gets called again. Instep 146, the remainder of the program operates in a normal manner. In asecond time through the device because of the no operation instruction,step 146 is executed directly after step 136. This aspect of theinvention is advantageous to prevent rewriting of the EEPROM needlessly.Thus, upon the operation of a spurious power supply the system does notneed to reset or rewrite the memory. As mentioned above, a typicalprogram EEPOM may be rewritten about 1,000 times in its useful life.Data EEPROM may be rewritten about 10,000 times.

[0057] Referring now to FIG. 12, as mentioned above, the presentinvention communicates two ways between the base station and each mobileunit 12. Of course, the specific application for which the mobile unitswill be used may dictate different command messages. During the courseof operations, it may be desirable to change the messages. For example,the messages may be changed upon initial power up, at the beginning ofthe day. This will allow crews to have updated messages for the day'swork. In FIG. 12, an example of display 36 is illustrated having variouscommands 148 a, 148 b, and 148 c.

[0058]FIG. 13 illustrates a method for programming the messages. In step150, the generic messages are programmed within the memory. This maytake place during manufacture of the device. In step 152, the system ispowered up within a system and a signal is sent to the base station. Thebase station in step 154 receives the signal and places the device onthe map display. The power up signal 152 may include or be used as aninquiry signal so that the base stations knows message changes may begenerated to the base. In step 154, the base stations broadcast messagechanges from the base station when receiving the power up signal in step152. The messages are received by the mobile unit in step 156. Theoperation of the system using the updated messages is performed in step158.

[0059] Referring now to FIG. 14, a more detailed operation of the methodfor operating a mobile unit is described. During operation, two-waycommunication is normally performed in step 160. In step 162, thewireless modem is turned off or held as described above. In step 164,the GPS is turned on. This routine prevents the wireless modem and theGPS from interfering with each other. In step 166, a time period iswaited for the GPS signal to be received. As an alternative, rather thana time period, a check for a coherent GPS signal may be used. In step168, the GPS receiver, once a signal is received, is turned off. In step170, the wireless modem is turned on or removed from the hold status. Instep 172 the message from the mobile unit is transmitted to the basestation. In step 174, the message is retained at the mobile unit and atime period is allowed to pass in step 174. In step 176, a check isdetermined whether a response has been received from the base station.If a response has not been received, the message is retained in step178. The message is retransmitted to the base station using the sequencein step 162 with older messages transferred first. Referring back tostep 176, if a response has been received from the base station, thechecksum associated with the response is checked in step 182. If theresponse does not have a proper checksum, then step 178 is executed. Instep 182, if a proper checksum has been received, the portable unitdetermines whether or not the sleep time of the GPS receiver has beenmodified. The sleep time is the amount of time between transmissions ofthe position messages from the GPS. When turning a unit on the sleeptime starts after an initial valid message (fix) is received. Themodified sleep time is checked in step 184. In step 186, the time periodto wait before checking the GPS receiver is waited in step 186 andthereafter step 182 is executed in which the wireless modem is turnedoff and the GPS is again checked. The battery life may also betransmitted. Formatting for the communication may be performed with thefollowing format:

[0060] $$$$$, DATE, TIME, XmitCount, Latitude, Longitude, PDOP, Type,ID, Battery %, (Message ID correctly received), (Acknowledge Code),Checksum

[0061] Where:

[0062] “$$$$$,” is the message header.

[0063] All dates and times are GMT. DATE is a 4 byte number, consistingof DMYY, where:

[0064] D=Day, 1-byte binary number from 1-31.

[0065] M=Month, 1-byte binary number from 1-12.

[0066] YY=Year, 2-byte binary number from 2002-2047.

[0067] TIME is a 3-byte number, consisting of HMS, where:

[0068] H=Hour, 1-byte binary number from 0-23.

[0069] M=Minute, 1-byte binary number from 0-59.

[0070] S=Seconds, 1-byte binary number from 0-59.

[0071] XmitCount is a 1-byte transmission counter tagged to eachmessage.

[0072] Latitude is a signed binary number in Motorola's binary format.It ranges from −324,000,000 to 324,000,000, corresponding to −90 to +90degrees. A positive number corresponds to north latitude.

[0073] Longitude is a signed binary number in Motorola's binary format.It ranges from −648,000,000 to 648,000,000, corresponding to −180 to+180 degrees. A negative number corresponds to west longitude.

[0074] PDOP is the Position Dilution of Precision, a single byte rangingfrom 0 to 255. A value of zero indicates that the GPS receiver does nothave a fix (a valid position). The values of 1-255 correspond to 0.1 to25.5.

[0075] Type is a 1-byte number that tells what type of transponder unitsent the message. Currently, there are five different recognized types:handheld unit, ground vehicle, fixed-wing aircraft, helicopter, and basestation.

[0076] ID is a unique ID number for each system. It is a 2-byte unsignedbinary number corresponding to the serial number of the unit.

[0077] Battery % is the percentage of battery life remaining. This1-byte number can be from 0-255, corresponding to 0% to 255%. Forsystems connected to an external power source, it is common to see abattery life of around 105-115%.

[0078] The “Message ID Correctly Received” field is a 2-byte numbercorresponding to the ID code of a message attached to an acknowledgefrom the base station. If the base station sends the unit apage/message, it does so by attaching it to an acknowledge message andtagging it with a non-zero ID code. When a field unit correctly receivesa message, it puts the ID code in this field on its next fixtransmission.

[0079] The “Acknowledge Code” is a 4-byte number for sending additionalinformation from the field unit to the base station. Note that this isalso the code used to send custom messages from the handheld unit to thebase station.

[0080] The Checksum is a 1-byte exclusive-OR of all of the bytes in themessage starting with the first byte in the DATE field (the month) andending with the last comma (before the checksum).

[0081] One version of the system may add GPS Height, 3 d and 2 d GPSSpeed, and GPS heading for the following, modified format:

[0082] $$$$$, DATE, TIME, XmitCount, Latitude, Longitude, GPS Height, 3d Speed, 2 d, Speed, GPS Heading, PDOP, Type, ID, Battery %, (Message IDcorrectly received), (Acknowledge Code), Checksum

[0083] Where:

[0084] GPS Height is a 4-byte number in Motorola's binary GPS heightformat, in cm 3 d Speed and 2 d Speed are 2-byte numbers in Motorola'sbinary GPS speed format in cm/s

[0085] GPS Heading is a 2-byte number in Motorola's binary GPS headingformat, in tenths of degrees, from 0 to 3599, corresponding to 0.0 to359.9 degrees true.

[0086] Notice that the commas separating each field are not reallynecessary for operation, but are quite useful during development of asystem using this protocol, since they make debugging, troubleshooting,and programming much easier. After development is complete, the commascan be removed to shorten the message length.

[0087] It should be noted that a constructed embodiment of the inventionis able to retain up to 19 stored position signals in step 178. When theoldest signal is received properly by the base station, the next oldestis attempted until a successful signal has been sent. Thus, the basestation provides an updated moving map of each of the positions of themobile units. The base station response consists of 5 bytes with thefollowing format: 0xff ID FixCount Page/Message-flag Checksum

[0088] Notice that there are no commas separating each byte, and alsonotice that the first byte is 255, or 0xff (hexadecimal). This number isused to indicate that the acknowledge message follows, and each handhelddevice, upon receiving 0xff, resets its acknowledge code parsingroutine. This also means that 0xff must not appear anywhere else in themessage, including in the checksum. This is done by eliminating all 0xffbytes from each serial number, by making sure the FixCount is never0xff, and by manipulating the bits in the Page/Message flag so that, itis never 0xff and the Checksum is never 0xff. Bit 6 of the Page/Messageflag Q is cleared (0) so that it can never be 0xff, and make bit 7 (themost significant bit) of the Page/Message flag whatever it takes to makethe Checksum bit 7=0, so that the Checksum can never be 0xff. Thisscheme has been tested and has been found to maximize the reliability of“round-trip” communications in the presence of noise, and where somebytes can get lost or corrupted. If bit 0 (the least significant bit) ofthe Page/Message flag is 1, then a message follows the Checksum with thefollowing format: Message ID <80 character ASCII message> Checksum

[0089] Again, notice that there are no commas in the response from thebase station. The message ID is a 2-/byte number that the handheld unitwill respond with in the “message ID correctly received” field of theoutgoing position message the next time a position update is sent. Thistells the base station that the message with the same ID was correctlyreceived by the handheld unit. The 80 character message is 4 lines of 20characters that the handheld unit displays on the text display uponreceiving it.

[0090] If bit 0 of the Page/Message flag is 0, but bit 1 of thePage/Message flag is 1, then an updated “sleep time” command follows.Recall that the sleep time is the time that the handheld unit turns offthe modem and turns on the GPS between position message transmissions.If bit 0 of the Page/Message flag is 1, indicating that a Page/Messagefollows, bit 1 is ignored, so the system cannot update the sleep timeand display a message simultaneously. If bit 0 is 0 and bit 1 is 1, thenthe following sleep time update format follows the acknowledge:

[0091] Sleep time Sleep time Sleep time

[0092] which is simply a 1-byte number, the sleep time, repeated threetimes. If the handheld unit does not receive the same number intriplicate, it is assumed that there was an error in updating the sleeptime and the command is ignored. The sleep time number is between 0 and255, and corresponds to the number of seconds times 2 that the systemwaits between position fix transmissions. Notice that a value of zerocorresponds to 256*2 or 512 seconds. A value of 1 is a special case thatactually does update at 1 Hz, but is typically only used for the HiVALin Field Test Range applications.

[0093] Notice that the outgoing handheld messages are pre-programmedmessages that are represented by codes in the 4-byte “Acknowledge Code”embedded in the position/fix message. There are over 4 billion possibleunique messages that could be represented by this 4-byte number, and itis unlikely that we would ever need to store more than 256, so one bytecan be used as the message and the other 3 bytes as parameters forfuture expansion.

[0094] Referring now to FIG. 15, there are two basic modes of operation.In a first mode of operation, updated position signals are continuouslydisplayed on the device. When messages are received, the message fromthe base station is displayed on the display. In a second mode ofoperation the user activates the button to transmit a message to thebase station. FIG. 15 illustrates the first mode of operation. In step200, a message from the base station is received. In step 202 themessage is displayed preferably so that the position information is nolonger present on the display. In step 204, an audible and visualindicator is provided. That is, the visual aspect of displaying themessage such as in step 202 and an audible indicator is activating thebeeper 64 shown in FIG. 4. In step 206, if the button is depressed to afirst position in step 206 acknowledging the message and released, step208 deactivates the ringing tone and resumes the default display in step210. Referring back to step 206, if the message is not acknowledged thereceived message is continually displayed in step 212 and the ringingtone continues in step 214. The system may also be set up so that thedepression of the button stays on the screen until the one single buttoninterface is released. A default display may be shown as follows: GPS  3dFix 3.2   0/12 03 Sep 2002 15:59:05 35° 08.1342′N 106° 44.3321′WB100%

[0095] Messages sent by the base station may take the form of:

[0096] Test Message.

[0097] Messages look like this on the LCD of the handheld unit

[0098] Such a message may be typed using a keyboard into a popup boxafter clicking on the desired unit to send it to. When the mobile unitreceives the message, the exact same messages L will be performed on theportable unit display. Alternating beeps between a ringing and warblingtone may also be used as the ringing tone. In one constructiveembodiment, if the user depresses the single button interface, theringing tone is changed to a single short beep to indicate partialacknowledgement. Status messages may also be displayed.

[0099] When the handheld unit sends its next position fix, the laptopdisplay may also update to show the updated position.

[0100] Referring now to FIG. 16, a second mode of operation describedabove is illustrated in flow chart form. In this embodiment, the defaultdisplay is displayed in step 216. If the button is not being depressedin step 218 the default display continues in step 216. If the button isdepressed, step 220 is activated. In step 220 a display timer (6seconds) is set. Thereafter, in step 222 a menu appears that has analternating top message to provide the user with an instruction to pressand hold to select a message to be sent. It should be noted that themenus may vary for each unit or unit type as the situation requires. Oneexample of a message display is illustrated in the format:

[0101] Press & Hold-Select

[0102] >Send Distress Call<

[0103] Request Evacuation

[0104] Water Drop Here

[0105] At this point the button is still depressed. When the button isreleased in step 222 in less than one second in step 224, the menuscrolls upward in step 226. The alternating message and menu iscontinued to be displayed in step 220. A message is selected in step 228by holding the button for more than one second (or other predeterminedtime) with a code corresponding to a highlighted message. Thehighlighted message may be between carats and may, for example, be thetop line of the display. In step 230 the message is transmitted to thebase station. In step 228, if the outgoing message has expired theposition is displayed by returning back to step 216. In step 232 anacknowledgement is waited for from the base station by the mobile unit.If the outgoing message is acknowledged in step 234, the text display onthe mobile unit may, for example, have the format:

[0106] >Send Distress Call<

[0107] acknowledged!

[0108] *****************

[0109] Click to resume . . .

[0110] Other features such as the beeper warbling three times atapproximately 0.2 intervals may also be generated. When the userreleases the button the status message such as that shown above iserased and the position information is provided in step 216. Referringback to step 232, if the signal is not acknowledged the mobile unit maydisplay an “not acknowledged display”, display the position informationfor a time in step 238, and retransmit the information in step 240. Whena message is sent to a base station, the base station number and themessage may be displayed in a popup window so that action may be takenby the base station operators. During the retransmission, aretransmission message may continually be displayed such as “will keeptrying every 20 seconds.” Tones may also continue to be generated toindicate the mobile unit is continually trying to transmit the messageto the base station.

[0111] While the invention has been described in connection with one ormore embodiments, it should be understood that the invention is notlimited to those embodiments. On the contrary, the invention is intendedto cover all alternatives, modifications, and equivalents, as may beincluded within the spirit and scope of the appended claims.

What is claimed is:
 1. A method of operating a communication devicehaving a transmitting device and a receiving device comprising: whilethe transmitting device is off, tuning on a receiving device; receivinga received signal; turning off the receiving device; and turning on thetransmitting device.
 2. A method as recited in claim 1 furthercomprising after receiving, waiting a predetermined amount of time.
 3. Amethod as recited in claim 2 wherein said predetermined amount of timecorresponds to a time for obtaining a position fix.
 4. A method asrecited in claim 1 further comprising transmitting the position signalto a base station; receiving a response signal from the base station;checking a checksum from the response signal.
 5. A method as recited inclaim 4 further comprising when the check sum is a proper checksum,changing a display on the device.
 6. A method as recited in claim 1wherein the device comprises a mobile unit.
 7. A method as recited inclaim 1 wherein the transmitting device comprises a wireless modem.
 8. Amethod as recited in claim 1 wherein the receiving device comprises aGPS receiver and wherein the received signal comprises a positionsignal.
 9. A method of operating a communication device comprising:holding operation of a wireless modem; turning on a GPS receiver;receiving a position signal; obtaining a position fix; turning off theGPS receiver; and turning on the wireless modem.
 10. A method as recitedin claim 9 wherein the step of obtaining a position fix compriseswaiting a predetermined amount of time
 11. A method as recited in claim9 further comprising transmitting the position signal to a base station.12. A method as recited in claim 11 further comprising receiving aresponse signal from the base station.
 13. A method as recited in claim12 further comprising checking a checksum from the response signal. 14.A method as recited in claim 13 further comprising storing theinformation until a checksum is received.
 15. A method as recited inclaim 14 further comprising when the check sum is a proper checksum,changing a display on the communication device.
 16. A method as recitedin claim 9 wherein the device comprises a mobile unit.
 17. Acommunication device comprising: a receiving device periodicallyreceiving a plurality of signals; a transmitting device transmittingmessages; and a controller coupled to the receiver and the modem, saidcontroller discontinuing operation of the transmitting device when thereceiving device is receiving one of the plurality of signals,thereafter said controller operating the transmitting device.
 18. Adevice as recited in claim 17 wherein the transmitter transmits the oneof the plurality of signals to a base station.
 19. A device as recitedin claim 18 wherein the transmitter receives a response signal from thebase station having a checksum.
 20. A device as recited in claim 19wherein said controller checking a checksum from the response signal.21. A device as recited in claim 20 further comprising a display, saidcontroller changing the display on the device when the checksum is aproper checksum.
 22. A device as recited in claim 17 wherein thetransmitting device comprises a wireless modem.
 23. A method as recitedin claim 17 wherein the receiving device comprises a GPS receiver.